import sys
N = int(input())
V = list(map(int, input().split()))
dp = [0] * N
if N == 1:
    print(V[0])
    sys.exit()
dp[0] = V[0]
dp[1] = max(V[1], V[0])
for i in range(2, N):
    dp[i] = max(dp[i-1], dp[i-2]+V[i])
print(dp[N-1])